As a conventional technique of calculating the homothetic ratio of two images, a technique disclosed in Japanese Patent Laid-Open No. 2003-248827 is known. In Japanese Patent Laid-Open No. 2003-248827, the homothety between a reference image and a check image is calculated to perform similarity collation (similarity comparison) between them. At this time, both the homothetic ratio and the translation amount of a comparison region between the projection waveforms of the reference image are calculated. Homothetic transformation and position correction are performed on the basis of the homothetic ratio and translation amount to achieve a detailed comparison.
In order to calculate the translation amount and homothetic ratio, they are estimated for combinations of the peak positions of the projection waveform of a reference image and those of the projection waveform of a check image. Estimate homothetic transformation parameters including translation amounts and homothetic ratios which are estimated for respective combinations are generated. Of the estimate homothetic transformation parameters, a parameter of high likelihood is determined as a homothetic transformation parameter.
However, in Japanese Patent Laid-Open No. 2003-248827, many combinations of the peak positions of the projection waveform of a reference image and those of the projection waveform of a check image must be used to estimate the translation amount and homothetic ratio. No sufficient number of peaks of the projection waveform may be obtained from an image having a small feature. To the contrary, many features require a long time for calculation processing. The peaks of the projection waveform may vary due to factors such as noise and a stain, failing to obtain an accurate result.
In this manner, simultaneous calculation of the translation amount and homothetic ratio has both a merit and demerit.
It is safer to robustly calculate the translation amount and homothetic ratio at different stages while avoiding the influence of factors such as noise and a stain, than to simultaneously calculate the translation amount and homothetic ratio. This calculation method is preferably employed to efficiently implement similarity comparison.
The present invention has been made to overcome the conventional drawbacks, and has as its object to provide an image processing apparatus capable of efficiently executing similarity comparison between images at high precision, a control method therefor, and a program.